1) Technical Field
The present invention generally relates to lifting gears such as cranes which use ropes such as high-strength fiber ropes. The invention in particular relates to a device for determining the discard state of such rope in use on such lifting gears, comprising a detection device for detecting at least one rope utilization parameter influencing the rope discard and an evaluation unit for evaluating the rope utilization parameter and for providing a discard signal in dependence on the rope utilization parameter evaluation.
2) Description of the Related Art
In recent times attempts are made in cranes to use high-strength fiber ropes made of synthetic fibers such as for example aramide fibers (HMPA), aramide/carbon fiber mixtures, high-modulus polyethylene fibers (HMPE) or poly(p-phenylene-2,6-benzobisoxazole) fibers (PBO) instead of the proven steel ropes that have been used for many years. The advantage of such high-strength fiber ropes resides in their low weight. With the same rope diameters and the same or higher tensile strengths, such high-strength fiber ropes are distinctly lighter in weight than corresponding steel ropes. In particular in high cranes with correspondingly large rope lengths this results in a greater weight saving, which feeds into the dead load of the crane and leads to correspondingly higher payloads with otherwise unchanged construction of the crane.
A disadvantageous property of such high-strength fiber ropes however is their breakage behavior or their failure without distinct, longer advance notice. While in steel ropes the wear is readily apparent and a failure is announced quite some time before, for example by the breakage of individual steel wires and by corresponding splicing, which easily is noted, high-strength fiber ropes hardly show any signs of excessive wear, which would easily be perceptible with the eye and would become apparent quite some time before the actual failure. In so far, there is a need for intelligent monitoring measures, in order to recognize the discard state of high-strength fiber ropes in good time.
From DE 199 56 265 B4 a device for monitoring the operation of hoisting winches on cranes is known, which determines the rope force of the hoisting rope and the lever arm of the hoisting rope on the rope winch and therefrom determines the load cycles acting on the rope winch, which are stored in a load spectrum counter. This load spectrum counter is integrated into the hoisting winch, in order to traceably preserve the history of the hoisting winch during removal and re-installation of the same. From EP 0 749 934 A2 there is furthermore known a load spectrum counter which determines the occurring load changes, for each load change determines the rope force applied to the hoisting winch, therefrom calculates the load spectrum and by including the so-called “Wöhler” curves calculates and indicates the remaining service life of the hoisting winch.
Such monitoring measures of the hoisting winch, however, cannot really reliably indicate the remaining service life or the discard state of a high-strength fiber rope, as the high-strength fiber ropes are subject to various loads and impairments influencing wear, which are independent of the loads acting on the winch, e.g. the deflection and bending loads of deflection pulleys, external shocks and blows to the rope, surface impurities of components in contact with the rope, etc. On the other hand, rigid specifications of the lifetime of high-strength fiber ropes hardly are compatible with each other in terms of the economic utilization of the actual lifetime and the necessary safety compliance, as in dependence on the conditions of use and the external influences on the high-strength fiber rope its service life and wear can fluctuate greatly.
From WO 2012/100938 A1 it furthermore is known to monitor several rope parameters of a high-strength fiber rope, which when approaching the discard state show characteristic changes. Even if a rope parameter shows no or no significant or no sufficiently strong change, the discard state can be recognized by monitoring further rope parameters, in particular when several parameters show changes. The detection unit of the device for recognizing the discard state comprises several, differently formed detection means for the magnetic, mechanical, optical and electronic detection of a plurality of different rope parameters, which individually or in combination with each other can be evaluated by the evaluation unit for recognizing the discard state. Despite the evaluation of several rope parameters, however, the problem remains that the discard state not always actually is given with the same changes of rope parameters or there is no rigid connection between individual changes of rope parameters and the discard state. Depending on the individual case, a change in the transverse compressive rigidity or a number of bending cycles can have a different meaning for the discard state.
Proceeding therefrom, it is the object underlying the present invention to indicate an improved device for determining the discard state of high-strength fiber ropes, which avoids disadvantages of the prior art and develops the latter in an advantageous way. Preferably a reliable, precise determination of the discard state should be achieved, which economically makes use of the remaining service life of the fiber rope without putting safety at risk and for this purpose can do with simple detection devices operating reliably also under severe conditions of use for construction machines.